QS3 2019 Question Session 2
Natalia Drichko (John Hopkins), Jun Zhu (PSU)
2019 NSF/DOE/AFOSR Quantum Science Summer SchoolJune 13, 2019
A. YesB. No
Does this response system work correctly?
Test of Response System
Question 0
A. Yes
Does this response system work correctly?
Test of Response System
Question 0
Yes this works
Topological Superconductivity
Question 1
1. We get a chain with a single Majorana mode
2. We cannot remove a single Majorana site because electrons (pairs of Majoranas) are the only physical degrees of freedom
3. The Hamiltonian becomes topologically trivial
4. Removing a single Majorana is not allowed by particle-hole symmetry
A) 1B) 2C) 3D) 4
What happens if we remove the last Majoranasite of a Kitaev chain in the topological phase?
Topological Superconductivity
Question 1
What happens if we remove the last Majoranasite of a Kitaev chain in the topological phase?
A) 1B) 2C) 3D) 4
1. We get a chain with a single Majorana mode
2. We cannot remove a single Majorana site because electrons (pairs of Majoranas) are the only physical degrees of freedom
3. The Hamiltonian becomes topologically trivial
4. Removing a single Majorana is not allowed by particle-hole symmetry
Topological Superconductivity
Question 2
1. There can be no state at zero energy
2. The bands at positive energy mirror the bands at negative energy
3. Crossing at zero energy is allowed
A) 1B) 2C) 3D) 1 and 2E) 2 and 3
Particle-hole symmetry in the Bogoliubov-de GennesHamiltonian implies
Topological Superconductivity
Question 2
1. There can be no state at zero energy
2. The bands at positive energy mirror the bands at negative energy
3. Crossing at zero energy is allowed
A) 1B) 2C) 3D) 1 and 2E) 2 and 3
Particle-hole symmetryin the Bogoliubov-de GennesHamiltonian implies
Topological Quantum Computing
Question 3
1. A pair of Majorana fermions
2. Topological degeneracy
3. Non-abelian statistics
4. A topological qubit
A) 1B) 2C) 3D) 4
The two ends of a single topological nanowire such as InAs or InSb realize
g1 g2
Topological Quantum Computing
Question 3
1. A pair of Majorana fermions
2. Topological degeneracy
3. Non-abelian statistics
4. A topological qubit
A) 1B) 2C) 3D) 4
The two ends of a single topological nanowire such as InAs or InSb realize
g1 g2
2D Heterostructures
Question 4
A) 1B) 2C) 3D) 1 and 2E) 2 and 3
1. Use highly purified carbon for graphite, and then exfoliate
2. Use CVD growth with purified carbon
3. Exfoliate graphene and then transfer it on boron nitride
How to improve properties of graphene?
2D Heterostructures
Question 4
A) 1B) 2C) 3D) 1 and 2E) 2 and 3
How to improve properties of graphene?
Intrinsic TMD
Question 5
A) 1B) 2C) 3D) 1 and 2E) 2 and 3
What are the effects of reducing the number of layers on the electronic structure of MoS2?
1. Electronic bands split into spin-up and spin-down bands for the single layer.
2. The band gap becomes a direct gap
3. For a single layer a Dirac cone is formed at the Fermi energy
Intrinsic TMD
Question 5
A) 1B) 2C) 3D) 1 and 2E) 2 and 3
What are the effects of reducing the number of layers on the electronic structure of MoS2?
2D TMD semiconductors
Question 6
1. 10 meV and 100 nm
2. 100 meV and 1nm
3. 10 meV and 1 nm
4. 100 meV and 100nm
5. 10 eV and 1 nm
A) 1B) 2C) 3D) 4E) 5
What is the (order of magnitude) binding energy and size of 1s excitons in a monolayer TMD semiconductor?
2D TMD semiconductors
Question 6
A) 1B) 2C) 3D) 4E) 5
What is the (order of magnitude) binding energy and size of 1s excitons in a monolayer TMD semiconductor?
1. 10 meV and 100 nm
2. 100 meV and 1nm
3. 10 meV and 1 nm
4. 100 meV and 100nm
5. 10 eV and 1 nm
2D TMD semiconductors
Question 7
A) 1B) 2C) 2 and 3D) 3 and 4E) 2, 3 and 4
Pump-probe Kerr rotation measurements of monolayer TMD probe the lifetime of X, and the time scale is Y.
1. X= e-h recombination time, Y= 1-10 ps
2. X= spin relaxation of electron, Y= 100 ns
3. X= spin/valley locked relaxation of hole,
Y= 1 us
4. X= interlayer exciton lifetime in a
WSe2/MoS2 heterostructure, Y = 1us
2D TMD semiconductors
Question 7
Pump-probe Kerr rotation measurements of monolayer TMD probe the lifetime of X, and the time scale is Y.
A) 1B) 2C) 2 and 3D) 3 and 4E) 2, 3 and 4
1. X= e-h recombination time, Y= 1-10 ps
2. X= spin relaxation of electron, Y= 100 ns
3. X= spin/valley locked relaxation of hole,
Y= 1 us
4. X= interlayer exciton lifetime in a
WSe2/MoS2 heterostructure, Y = 1us
Valleytronics
Question 8
A) 1B) 2C) 3D) 4E) 5
1. Sub 14nm device size2. Operating frequency above 4 GHz3. Strong exciton binding energy4. Atomically thin channel5. Reduced switching energy
Exciton-based valleytronic computing could offer a material improvement over existing silicon CMOS due to
Valleytronics
Question 8
A) 1B) 2C) 3D) 4E) 5
1. Sub 14nm device size2. Operating frequency above 4 GHz3. Strong exciton binding energy4. Atomically thin channel5. Reduced switching energy
Exciton-based valleytronic computing could offer a material improvement over existing silicon CMOS due to
Topological Valleytronics in Bilayer Graphene (Zhu Lab)
J. Li… JZ, Nature Nano. 11, 1060 (2016).J. Li… JZ, Science 362, 1149 (2018).
1. First make valley-momentum locked topological 1D channels in bilayer graphene (quantum valley Hall effect)
2. Change the topology to control the way valley and momentum are locked.
3. Topological valley valve and beam splitter
S
- D+D
D
DD
K K’
https://youtu.be/thJpzhYkO7Y
https://www.youtube.com/watch?v=iOsout7aVGc
- D +D
https://www.youtube.com/watch?v=Bj6IIDBadME&t=1s
Spin Transfer Torque Based Magnetic Random Access Memory
Question 9
1. Switching speed
2. Data retention over a long period of time
3. Reliability of switching (error rate < 10-9)
A) 1B) 3C) 1 and 2D) 2 and 3E) All of them
What are the fundamental challenges of STT-switched MTJs
Spin Transfer Torque Based Magnetic Random Access Memory
Question 9
A) 1B) 3C) 1 and 2D) 2 and 3E) All of them
What are the fundamental challenges of STT-switched MTJs
1. Switching speed
2. Data retention over a long period of time
3. Reliability of switching (error rate < 10-9)
Photons as qubits
To make a qubit out of a qdot-cavity system, we need to
Question 10
1. Overlap the photonic cavity with the quantum dot spatially
2. Achieve resonance between the emission modes of the qdot and the modes of the cavity
3. Engineer strong coupling between the two
4. Reduce loss of the cavity
A) 1 and 2B) 2 and 3C) 1, 2 and 3D) All of them
Photons as qubits
To make a qubit out of a qdot-cavity system, we need to
Question 10
1. Overlap the photonic cavity with the quantum dot spatially
2. Achieve resonance between the emission modes of the qdot and the modes of the cavity
3. Engineer strong coupling between the two
4. Reduce loss of the cavity
A) 1 and 2B) 2 and 3C) 1, 2 and 3D) All of them